The coupling or interconnecting of adjacent pipe ends to form a continuous fluid conveying line is an area which embraces a great variety of problems. First, the coupling must be economical to produce and easily and quickly installed without expensive equipment and highly skilled employees. Second, it must seal the joint against escape of fluids and against intrusion of outside contaminants. Third, it must provide electrical continuity through the coupling from pipe end to pipe end, particularly where used underground for gas or fuel transmission and it is essential to provide cathodic protection, or above ground where the pipe must be grounded as in gasoline or jet fuel transmission. Fourth, it must be capable of use in a great variety of applications, for example, low or high pressures, lined or unlined pipe, and straight line and non-straight line applications. Fifth, it must be strong and safe, that is, its form and construction must be such that it can be designed to handle the most extreme conditions of pressure and the like which would be likely to be encountered in the service for which designed. These several problems and criteria are well known in the trade and a great variety of couplings have been proposed over the years for their solution.
The problem of sealing pipe joints has often been approached by providing gaskets to seal all possible pathways from the interior of the pipe sections to the exterior of the coupling through which fluid might escape. Typically, a coupling for joining two abutting pipe ends either includes two semi-cylindrical pieces which are fastened together to clamp down on the pipe ends, or a single cylindrical piece having an axial slit which allows the coupling to be opened by an amount sufficient to fit over the pipe ends. A major portion of the sealing function can be accomplished by placing annular gasket members, such as O-rings, around the respective pipe sections near their ends. However, this leaves the problem of sealing the fluid pathway through the axial joints in the coupling itself. One approach, as shown in U.S. Pat. No. 2,913,262 and U.S. Pat. No. 3,153,550, has been to provide an axial gasket member extending between the O-rings within the axial joints of the coupling. Another approach, as shown in U.S. Pat. No. 1,607,943 and in French Pat. No. 355,620, has been to provide an annular central web connecting the O-rings, completely surrounding the pipe ends and spanning the gap between the pipe ends. This solution has the disadvantage that if the web is physically pressed by the coupling against the pipe ends, sharp or ragged pipe ends may lead to early deterioration of the gasket. If the web is not pressed against the pipe ends by the coupling, as is the case in the above-identified French patent, then the pressure of fluid within the pipes must be relied upon to maintain the seal of the joint.